In cryogenic refrigerators, such as the Stirling and Gifford-MacMahon cycle refrigerators, a displacer piston reciprocates within a cold finger cylinder betweem warm and cold ends. An internal displacer regenerator or an external regenerator carries working fluid between the warm and cold ends. Refrigeration gas is cooled as it flows through the regenerator and is then further cooled by expansion in an expansion chamber at the cold end of the displacer. The thus cooled gas is then able to absorb heat from a load mounted to the refrigerator station or stations of the cold finger.
As was noted in Chellis et al., U.S. Pat. No. 3,600,903, to provide maximum heat exchange, and thus a low thermal gradient, between the load and the refrigeration gas, it is desirable that the gas contact a large heat transfer surface at each refrigeration station. However, when the displacer moves to the cold end the expansion chamber should be very small so that most gas is exhausted through the regenerator. For that same reason, the void volume in the gas flow path between the regenerator and the expansion chamber should be very small. To obtain the high transfer surface with low void volume, Chellis et al. provided narrow fluid passages along the outer walls of the cold finger. Refrigeration gas flowing from the regenerator to the expansion chamber flowed through those narrow passages.
This invention incorporated the basic principles of Chellis et al. in that the heat exchange efficiency of a cold finger is improved by providing a large heat transfer surface with high heat transfer coefficient but with minimum void volume.
An object of the invention is to provide a cold finger heat exchange assembly which allows for exceptional ease in the manufacture of the refrigerator units.
A further object of the invention is to provide a heat exchanger assembly which offers design flexibility with respect to heat transfer surface and void volume as required for any particular application.